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Microgravity Studies of Liquid-Liquid Phase Transitions in Alumina-Yttria Melts (January 31, 2004)

Author: Weber, Richar
Subject: GRID COMPUTING (COMPUTER NETWORKS); NASA PROGRAMS; SUPERCOMPUTERS; ARCHITECTURE (COMPUTERS); CENTRAL PROCESSING UNITS; PROTOTYPES; JAVA (PROGRAMMING LANGUAGE); COMPUTER SYSTEMS PROGRAMS
Year: 2004
Language: English
Book contributor: NASA
Collection: nasa_techdocs

Description

The scientific objective of this research is to increase the fundamental knowledge base for liquid- phase processing of technologically important oxide materials. The experimental objective is to define conditions and hardware requirements for microgravity flight experiments to test and expand the experimental hypotheses that: 1. Liquid phase transitions can occur in undercooled melts by a diffusionless process. 2. Onset of the liquid phase transition is accompanied by a large change in the temperature dependence of melt viscosity. Experiments on undercooled YAG (Y3A15012)- and rare earth oxide aluminate composition liquids demonstrated a large departure from an Arrhenian temperature dependence of viscosity. Liquid YAG is nearly inviscid at its 2240 K melting point. Glass fibers were pulled from melts undercooled by ca. 600 K indicating that the viscosity is on the order of 100 Pans (1000 Poise) at 1600 K. This value of viscosity is 500 times greater than that obtained by extrapolation of data for temperatures above the melting point of YAG. These results show that the liquids are extremely fragile and that the onset of the highly non-Arrhenian viscosity-temperature relationship occurs at a temperature considerably below the equilibrium melting point of the solid phases. Further results on undercooled alumina-yttria melts containing 23-42 mole % yttrium oxide indicate that a congruent liquid-liquid phase transition occurs in the undercooled liquids. The rates of transition are inconsistent with a diffusion-limited process. This research is directed to investigation of the scientifically interesting phenomena of polyamorphism and fragility in undercooled rare earth oxide aluminum oxide liquids. The results bear on the technologically important problem of producing high value rare earth-based optical materials.

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Identifier:	nasa_techdoc_20040046907
Document-source:	CASI
Documentid:	20040046907
Nasa-center:	Marshall Space Flight Center
Online-source:	http://wayback.archive-it.org/1792/20100201002539/http://hdl.handle.net/2060/20040046907
Original-nasa-rights:	Unclassified; No Copyright; Unlimited; Publicly available;
Updated-added-to-ntrs:	2008-06-02
Licenseurl:	http://creativecommons.org/licenses/publicdomain/
Mediatype:	texts
Rights:	Public Domain
Identifier-access:	http://www.archive.org/details/nasa_techdoc_20040046907
Identifier-ark:	ark:/13960/t9d51ht5g
Ppi:	300
Ocr:	ABBYY FineReader 8.0